1. Field of the Invention
This invention relates to a thermoelectric module such as, for example, a Peltier module.
2. Description of the Related Art
The thermoelectric effects are phenomena that occur between electric energy and temperature. The Peltier effect is one of the thermoelectric effects, and the Peltier junctions convert electric current to temperature differences. A Peltier module includes plural Peltier junctions, and electric current flows through the plural Peltier junctions so as to produce the temperature differences. Thus, the Peltier module is a sort of thermoelectric module.
A typical example of a thermoelectric module such as the Peltier module includes a pair of electrically insulating substrates opposed to each other, and metal electrodes are formed on the inner surfaces of the electrically insulating substrates. The metal electrodes are spaced from one another on each inner surface, and, accordingly, are electrically isolated by the electrically insulating substrate. The metal electrodes on one inner surface are offset from the metal electrodes of the other inner surface, and p-type semiconductor columns and n-type semiconductor columns are alternately connected between the metal electrodes on one inner surface and the metal electrodes on the other inner surface. Thus, the junctions between the metal and the p-type semiconductor are alternated with the junctions between the metal and the n-type semiconductor in the electric current path.
While electric current is flowing through the electric current path, the electric current alternately passes the junctions between the metal and the p-type semiconductor and the junctions between the metal and the n-type semiconductor, and temperature differences take place between the electrically insulating substrates.
The thermoelectric module has found a wide variety of applications such as, for example, an electric refrigerator and a cooling box. One of the reasons why the thermoelectric module is used in refrigerators is that the manufacturers were prohibited from using freon as the refrigerant, because freon has seriously damaged the ozone layer. The thermoelectric module is expected to transfer thermal energy under severe conditions. For example, purchasers generally request the manufacturer of the thermoelectric module to enhance the cooling efficiency and the mechanical strength. However, the prior art thermoelectric module merely achieves a low converting efficiency, and does not satisfy the purchasers"" requests. Thus, a problem inherent in the prior art thermoelectric module is the low converting efficiency.
It is therefore an important object of the present invention to provide a thermoelectric module, which achieves a high converting efficiency.
The present inventors contemplated the problem inherent in the prior art thermoelectric module, and noticed the air filling the space in the array of the semiconductor columns. The present inventors investigated prior art thermoelectric modules to see what factor had serious influences on the current-to-temperature difference characteristics of the thermoelectric module.
The present inventors measured the dimensions of the prior art thermoelectric modules. The prior art thermoelectric modules had the same structure as that described hereinbefore. The present inventors calculated the area of the inner surface and the total contact area between the semiconductor columns and the metal electrodes, and particularly observed the ratio of the total contact area to the area of the inner surface, wherein the ratio represents the amount of air filling the space. The results are tabulated below.
The present inventors fabricated thermoelectric modules which had a ratio greater than that of the prior art thermoelectric modules. The thermoelectric modules of the present invention achieved a converting efficiency higher than that of the prior art thermoelectric modules. The present inventors therefore concluded that the amount of air filling the space had strong influences on the converting efficiency. Although there was a limit on the density of the metal electrodes in the inner surfaces of the electrically insulating substrates, the limit was varied with the development of the fabrication technologies. The present inventors found a criticality at a ratio of 0.42.
The present invention was made on the basis of the above-described discovery, and proposes to increase the ratio of the total contact area to the area of the inner surface to at least 0.42.
In accordance with one aspect of the present invention, there is provided a thermoelectric module comprising an electrically insulating substrate structure having a major surface and plural thermoelectric junctions arranged on said major surface, connected to one another so as to produce temperature differences on said major surface and including semiconductor elements having cross sections respectively, and the ratio of the total area of said cross sections to an area of said major surface is equal to or greater than 0.42.